Take a portion of shadow, preferably with a dark mountain frame in the background. Mix it a little with a forbidden forest, but keep some unfriendly grass as a basis. And then a topping of clouds, but let them float. Then break then up with a gust of cold wind, mixing them a little and making everything a little uncertain. Place it all in front of a grey solid lid with no movement and then perhaps mix it all up with heavy drops of rain, although they can come later. Of course the highlight of the dish is when a crash of thunder arrives together with branches of illuminating light. That is my recipe for a thunderous slice of cake. Oh and do not forget a sprinkle of hailstones.